1. Field of the Invention
The invention generally concerns an apparatus for raising and lowering boats, and more particularly relates to an improvement employing flotation elements which can be raised and lowered by means of pumping water in or out, with the entire apparatus being adjustable to accommodate boats of different dimensions.
2. Discussion of the Prior Art
Apparatus of the general type to which the present invention relates is known from German patent 4,214,019, for example. According to this known publication, the hull of the ship to be raised is run onto a floating cushion that is subsequently inflated to raise the hull out of the water.
German patent 4,426,194 discloses another device for raising boats in water, where the known floating cushion principle is also combined with a magnetic holding device that is in contact with a (metallic) ship's hull and is secured there with suitable magnetic plates.
German utility model GM 9,312,336 concerns another device that is also based on the principle of a float that can be flooded and vented.
All these known apparatuses have in common the fact that their object is to raise a hull floating in water out of the water so the hull is raised above the water line while docked.
This concept offers some major advantages for winter boat storage since boats that are used with the known devices need no longer be dry docked. Likewise, these designs also have advantages because the underwater paint is exposed to water only when the hull is actually in use.
However, the known devices have the disadvantage that they do not keep the hull safe enough from accidents. In particular, there is a lack of stability when pumping up a boat--in other words, when lifting the hull out of the water.
Especially with the device according to German patent 4,214,019, the center of gravity of the boat is precisely in the middle of the inflatable cushions, which has the disadvantage that when the hull is lifted, it tends to tilt to the side.
A disadvantage of German patent 4,426,194 is that the float should be in contact with the outside of the hull, thus leading to a great increase in the total required width of the entire device, which consequently takes up a great deal of space in the water, although that is not desirable.